1. Field of the Invention
The present invention relates to a circuit breaker which is used to make and break a low voltage circuit or protect such low voltage circuit and, in particular, to a make-and-break mechanism for making and breaking the contact of a movable contact member.
2. Description of the Related Art
Conventionally, as a make-and-break mechanism of the above type for use in a circuit breaker, there is known a make-and-break mechanism which comprises: an operation handle rotatably supported on a frame composed of a cover plate and a back plate through a handle shaft; a make-and-break lever rotatably supported on a case through a make-and-break shaft and energized in one direction by a main spring; a mechanism member for transmitting the operation of the operation handle to the make-and-break lever; a latch having one end connected to the operation handle through the above handle shaft; a U-shaped pin disposed so as to bridge over the latch and mechanism member; and, a latch receiver rotatably supported on the above frame through a fulcrum shaft and, in the on state of the make-and-break mechanism, capable of securing the other end of the latch, wherein, in case where the secured condition of the latch by the latch receiver is removed due to the operation of an overcurrent detect portion of the make-and-break mechanism (a trip operation), the make-and-break lever is driven to an off position due to the stored energy of the main spring to thereby break the contact of a movable contact member, and, during this operation, that is, during the trip operation, an alarm output plate, which is disposed in the make-and-break mechanism so as to slide along the cover plate, is moved upwardly from a wait position to thereby operate an alarm contact.
Now, FIG. 7 is a front view of a conventional make-and-break mechanism including the above-mentioned alarm output plate, showing the on state thereof. In FIG. 7, although the alarm output plate 56 is energized upwardly by an output plate spring 70 consisting of a tension spring interposed between the alarm output plate 56 and a cover plate 27 consisting of the support frame of the make-and-break mechanism, the engaging portion 56a of the alarm output plate 56 is secured by a latch receiver 47 for securing a latch 34, whereby the alarm output plate 56 is held at a wait position shown in FIG. 7. The latch receiver 47 is rotatably supported on the support frame of the make-and-break mechanism through a projecting shaft 47a formed integral with the latch receiver 47 in the right and left direction and is energized clockwise by a return spring 50 which is inserted between the latch receiver 47 and cover plate 27.
Also, in FIG. 7, between the cover plate 27 and a pin 39 which connects an operation handle 26 to the mechanism member 36 of the make-and-break mechanism, there is provided a handle spring 59 which consists of a tension spring, while the operation handle 26 is energized clockwise. Further, an accessory linking plate 71 is guided to and held by the cover plate 27 in such a manner that it can be slided in the right and left direction, while the leading end of the accessory connecting plate 71 is opposed to the latch receiver 47. Between the accessory linking plate 71 and cover plate 27, there is provided a return spring 72 consisting of a tension spring.
The structure and operation of the make-and-break mechanism shown in FIG. 7 are substantially the same as those of the present invention which will be described hereinafter, and thus the detailed structure and operation thereof will be given through the detailed description of a mode for carrying out the present invention. That is, here, description will be given below of the trip operation of the make-and-break mechanism shown in FIG. 7. In the on state shown in FIG. 7, in case where an overcurrent flows in a circuit breaker, an overcurrent detect portion (not shown) is operated to push the upper end of the latch receiver 47 in the left direction, thereby rotating the projecting shaft 47a thereof counterclockwise. This removes the secured condition of the latch 34 by the latch receiver 47. As a result of this, a make-and-break lever 25 rotatably supported on the case through a make-and-break shaft 24 is driven or rotated due to the energy that is stored in a main spring 64, which breaks the contact of a movable contact member (not shown) (that is, trip operation). At the same time, the operation handle 26 rotatably supported by a handle shaft 31 is driven or rotated clockwise by the spring force of the handle spring 59, so that the operation line of the handle spring 59 stops at a position passing through the center of the handle shaft 31. This position is a trip display position and, at this position, the operation handle 26 is held in the horizontal attitude. This horizontal attitude of the operation handle 26 shows the generation of the trip operation.
Also, due to the above-mentioned rotation of the latch receiver 47, the secured position of the alarm output plate 56 is also removed at the same time and thus the alarm output plate 56 is moved upwardly by the spring force of the output plate spring 70. As a result of this, an alarm contact (not shown), which is disposed so as to be operated in linking with the alarm output plate 56, is operated, so that a trip signal is issued to the outside. On the other hand, in case where the accessory linking plate 71, which is used to operate or turn off the circuit breaker remotely by a voltage trip device, is pushed in the right direction against the return spring 72 by the voltage trip device (not shown), the latch receiver 47 is driven or rotated counterclockwise, which, similarly to the above-mentioned case, breaks the contact of the movable contact member.
In the above-mentioned make-and-break mechanism, conventionally, the alarm output plate 56 is normally secured by the latch receiver 47 and, at the same time, in the trip operation, the alarm output plate 56 is moved from the wait position by the output plate spring 70. Because of this, to the latch receiver 47, there are applied a load from the latch 34 as well as a load from the alarm output plate 56, which, in the trip operation, requires a large load force to drive or rotate the latch receiver 47. This leads to the increased size of the overcurrent detect portion as well as makes it easy to cause variations in the tripping characteristic. Also, the alarm output plate 56 requires an exclusive member, that is, the output plate spring 70; and, further, there are necessary another exclusive members which are used when an off operation is carried out by the voltage trip device, that is, the accessory linking plate 71 and its return spring 72. That is, the conventional make-and-break mechanism requires a large number of parts.